1. Field of the Invention
This invention relates generally to the field of plasma processing, and more particularly to capacitively coupled discharge plasma reactors.
2. Description of Related Art
Capacitive discharge plasma reactors are widely used to process semiconductor substrates, display substrates or the like. In these reactors, a plasma is formed when a gas (or gas mixture) is energized, leaving a mixture of charged and uncharged particles. The plasma can then be used to etch or form a deposit on a substrate.
A typical capacitive discharge plasma reactor uses a high-frequency electrode and a low-frequency electrode to generate plasma. These two electrodes are placed opposed to one another, spaced a short distance apart within a sealable chamber. This placement of the two electrodes forms a classic parallel plate capacitor, in which the low-power electrode acts as a holder (i.e., a chuck) for the workpiece to be processed.
During the operation of the plasma reactor, a gas or mixture of gases is introduced into the sealable chamber, and alternating current (AC) power is applied to the high-frequency electrode to generate the plasma. The power applied to the high-frequency electrode is typically in the radio frequency (RF) range, for example, 60 MHz. Typically, lower frequency AC power, 2 MHz for example, is applied to the low-frequency electrode in order to provide the workpiece with some bias, which modulates the effect of the plasma on the workpiece. This modulation occurs because the application of power to both the electrodes generates an electric field between them, thus influencing the characteristics of the charged particles of the plasma that strike the workpiece.
The plasmas generated by such plasma reactors are nonlinear; that is, at typically applied power levels, the impedance (resistance to electrical current flow) of the plasma is not directly proportional to the applied voltage. This nonlinearity causes the electrical properties of the plasma to be nonuniform. For example, several power frequencies (i.e. harmonics of the drive frequencies) can be present in different portions of the same plasma due to the nonlinear behavior of the plasma sheaths, even if only a single power frequency was used to generate the plasma. The use of such a nonuniform plasma can result in a workpiece that is not uniformly processed. A nonuniformly etched workpiece is undesirable in most plasma processing, and in many cases can have poor yield, or must be discarded.
The present invention provides an apparatus and a method of generating and controlling a plasma formed in a capacitively coupled plasma source having a plasma electrode and a bias electrode. The plasma electrode includes a plurality of sub-electrodes that are electrically insulated from one another. The plasma is formed in a plasma region between the plasma electrode and the bias electrode.
The method includes providing a radio frequency plasma generating electric power to the plasma electrode. The method also includes providing a radio frequency bias electric power at a lower frequency than the plasma generating radio frequency electric power. A first portion of the bias electric power is provided to the bias electrode, and a second portion of the bias electric power is provided to the plasma electrode.
The apparatus includes a capacitively coupled plasma source having a plasma electrode and a bias electrode. The plasma electrode includes a plurality of sub-electrodes that are electrically insulated from one another. The plasma electrode is spaced from the bias electrode by a plasma region in which the plasma is formed. The apparatus also includes a radio frequency plasma generating electric power supply in electrical communication with the plasma electrode, and a radio frequency bias generating electric power supply in electrical communication with the bias electrode and the plasma electrode.